1. Field of the Invention
This invention relates to the field of vapor deposition of films on substrates. More particularly, the field of this invention involves the vapor deposition of epitaxial films, for example silicon dioxide and like films, on exposed surfaces of articles, such as silicon wafer substrates commonly used in the electronics industry. Gaseous chemical reactants are brought into contact with a heated substrate within a reaction chamber the walls of which are transparent to radiant heat energy transmitted at a predetermined short wave length. A susceptor, which absorbs energy at the wavelength chosen, supports the substrate to be coated and heats the same as a result of its absorption of the heat energy transmitted into the reaction chamber from the radiant heat source employed.
2. Description of the Prior Art
While substrates, such as silicon wafers, have been coated heretofore with epitaxial films, such as silicon dioxide or like films, so far as is known, the specific and improved vapor deposition procedure and apparatus disclosed herein are novel. The apparatus and process of this invention are effective to produce uniform film coatings on substrates under controlled conditions so that coated substrates of high quality and excellent film thickness uniformity are producible within closely controlled limits.
In chemical deposition systems, it is highly desirable to carry out the deposition reaction in a cold wall type reaction chamber. By maintaining the reaction chamber walls in the unheated state, such walls receive little or no film deposition during substrate coating. Cold wall systems are additionally desirable because they permit the deposition of high purity films, such as silicon dioxide films. Impurities can be evolved from or permeate through heated reaction chamber walls. Because such impurities would interfere with and adversely affect the purity of the substrate coating, cold wall reaction chambers are employed to preclude such impurity evolution or permeation.
To avoid such problems, chemical deposition processes have been developed heretofore which permit heating of a substrate positioned within a reaction chamber without simultaneously heating the reaction chamber walls. Heretofore, the most successful of such processes involved the use of radio frequency (RF) induction heating of a conducting susceptor positioned within the reaction chamber, the walls of which were formed of non-conducting or insulating material. For example, RF heating of a graphite susceptor within a quartz reaction chamber for depositing epitaxial silicon films has been known generally heretofore.
However, such an RF heating technique, while it generally produces the stated objective in a cold wall reaction chamber, has several inherent and important disadvantages which make the same undesirable under many circumstances. For example, an expensive and bulky RF generator is required which is very space consuming and which must be located close to the epitaxial reactor. Also, the high voltages required with the RF coils produce substantial personnel hazards, and RF radiation from the RF coils can and frequently does interfere with adjacent electrical equipment. Furthermore, such an RF procedure requires the utilization of an electrically conducting susceptor for supporting the substrates to be heated. Also, RF systems are considerably more expensive overall than the simplified radiation heated system disclosed herein which were designed to replace the RF systems utilized heretofore.